The present invention relates to impact printing apparatus such as is used for computer printout and to ribbon cartridges for use with impact printing apparatus.
A common type of impact printer used for computer printout is known as a dot matrix printer. In this type of printer the characters are formed by selective printing of a number of dots arranged in a matrix formation. The dots are printed by selectively operating a number of print wires to cause the ends of the wires to strike an inked ribbon against a paper web supported by a platen. The print wires are contained within a print head supported on a carriage which travels parallel to the width of the paper web so as to print a line of characters across the web.
For convenience in replacing the ribbon, it is commonly contained within a replaceable cartridge structure. The cartridge includes means for guiding the ribbon from a storage region in the cartridge through a printing position in which the ribbon lies between the print head and the platen and thence back to the storage region. At the printing position, the length of the ribbon lies parallel to the line of printing and the ribbon is fed to present fresh portions of the ribbon to the print head during a series of printing operations. The ribbon may be fed from a supply reel in the cartridge to a take-up reel in the cartridge, or the ribbon may be formed as an endless band engaged by pinch rolls to feed the ribbon. In the latter arrangement, the ribbon is stored as a plurality of folded loops in the storage region of the cartridge.
Often, printing is required to be in only one colour, usually black, in which case the ribbon is black throughout its width. However there is a need to be able to print in any of a number of different colours selectable during the printing of a single sheet. In order to provide for such multi-colour printing, the ribbon carries the different colours in inked bands extending side by side along the length of the ribbon, each band being of sufficient width to accommodate the height of a character being printed. The required colour is selected by transverse movement of the ribbon, adjacent the print head, so as to interpose the band of the required colour between the print head and the paper. When using a single colour ribbon, it is common to provide a ribbon of greater width than the height of the characters to be printed and to obtain economy in usage of the ribbon by transverse movement of the ribbon in a series of steps whereby the full width of the ribbon is utilised.
It will be appreciated that although transverse movement of the ribbon is effected for both single and multi-colour ribbons the movement for single colour ribbons is a continuous series of step movements whereas for multi-colour ribbons the movement is from one band to any other band and only occurs when a change of colour is required. It is desirable that the printing apparatus should accommodate both single colour and multi-colour ribbon cartridges and that the appropriate drive means is put into operation dependant upon the ribbon type contained within the cartridge.